In order to enable the increasing data transmission needs to be answered, also wireless data transfer services have been improved. In addition to circuit-switched data services, a packet-switched General Packet Radio Service (GPRS) has also been standardized in the GSM system particularly for transferring Internet Protocol (IP) data. A network supporting the GPRS service comprises a Gateway GPRS Support Node (GGSN) and a Serving GPRS Support Node (SGSN). The SGSN is responsible for serving mobile stations MS connected to the GPRS network in its service area, transmitting and receiving data packets from such mobile stations and for monitoring the location of the mobile stations in its service area. When a mobile station MS is connected to the GPRS network, and more precisely to the SGSN, a mobility management context has to be created for the MS; in the GPRS network this function is called GPRS Attach. The GGSN operates as a gateway between the GPRS network and an external Packet Data Network (PDN). External data networks may include e.g. the GPRS network of another network operator, the Internet, X.25 network or a private local area network.
In order to enable packet-switched data to be transmitted between the mobile station and the network, a Packet Data Protocol (PDP) context has to be activated for the mobile station. In the PDP context activation, the MS is tied to a PDP address (typically an IP address), which is used for communicating with external networks. The state of the MS PDP context is then changed to ACTIVE. Since radio resources are consumed only during data transmission, a GPRS mobile station may have its PDP context activated all the time while being connected to the network. When connecting to the GPRS network, mobile stations can also be arranged to automatically activate the PDP context as well.
The GPRS mobile stations can be divided into three classes: class A mobile stations can simultaneously provide both a GSM call and GPRS data transfer, class B mobile stations only enable either a GSM connection or a GPRS service to be active at a time, and class C mobile stations only support the GPRS. A class B mobile station can detect an incoming GSM call also when the PDP context is active. In order to enable a GSM call to be established, a GPRS service is suspended (GPRS suspension), which means that in the mobile station and the GPRS network, data is prevented from being transmitted to the particular mobile station. Applications utilizing the GPRS service are provided (in the mobile station or e.g. in the application server of the network) with different time supervision features. Message arrival times are monitored, and if no reply nor a next message is received within a predetermined time-out period, the application interprets the connection to be lost, in which case the application cannot be continued even if the GPRS service could be continued after the GSM call has been terminated. It can be particularly harmful to suspend a service e.g. in a banking service application.